From: Max Kellermann Date: Tue, 28 Jan 2025 13:39:24 +0000 (+0100) Subject: io_uring/io-wq: do not use bogus hash value X-Git-Tag: v6.15-rc1~124^2~42 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=486ba4d84d62e92716cd395c4b1612b8ce70a257;p=thirdparty%2Fkernel%2Flinux.git io_uring/io-wq: do not use bogus hash value Previously, the `hash` variable was initialized with `-1` and only updated by io_get_next_work() if the current work was hashed. Commit 60cf46ae6054 ("io-wq: hash dependent work") changed this to always call io_get_work_hash() even if the work was not hashed. This caused the `hash != -1U` check to always be true, adding some overhead for the `hash->wait` code. This patch fixes the regression by checking the `IO_WQ_WORK_HASHED` flag. Perf diff for a flood of `IORING_OP_NOP` with `IOSQE_ASYNC`: 38.55% -1.57% [kernel.kallsyms] [k] queued_spin_lock_slowpath 6.86% -0.72% [kernel.kallsyms] [k] io_worker_handle_work 0.10% +0.67% [kernel.kallsyms] [k] put_prev_entity 1.96% +0.59% [kernel.kallsyms] [k] io_nop_prep 3.31% -0.51% [kernel.kallsyms] [k] try_to_wake_up 7.18% -0.47% [kernel.kallsyms] [k] io_wq_free_work Fixes: 60cf46ae6054 ("io-wq: hash dependent work") Cc: Pavel Begunkov Signed-off-by: Max Kellermann Link: https://lore.kernel.org/r/20250128133927.3989681-6-max.kellermann@ionos.com Signed-off-by: Jens Axboe --- diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index ba9974e6f5213..6e31f312b61a1 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -604,7 +604,9 @@ static void io_worker_handle_work(struct io_wq_acct *acct, do { struct io_wq_work *next_hashed, *linked; unsigned int work_flags = atomic_read(&work->flags); - unsigned int hash = __io_get_work_hash(work_flags); + unsigned int hash = __io_wq_is_hashed(work_flags) + ? __io_get_work_hash(work_flags) + : -1U; next_hashed = wq_next_work(work);